On sliding doors for so-called minibuses and elsewhere there is a demand for power door functions. The desired characteristics of a power door opening are wide-ranging. Examples of the desired characteristics include the requirement that the opening time should be relatively short, approximately 4–8 seconds, and that the available power must be sufficient both to close and to open the door even when the vehicle is standing on an inclined plane. Furthermore it must be possible to open the door manually, in the absence of power or in an emergency, for example. A power opening and closing apparatus should furthermore be easy to install on a number of different vehicles or types of vehicle. Various examples of apparatus for opening and closing sliding doors are demonstrated, for example, in U.S. Pat. No. 4,640,050, U.S. Pat. No. 5,316,365, U.S. Pat. No. 5,809,696, U.S. Pat. No. 5,833,302, U.S. Pat. No. 6,038,818, U.S. Pat. No. 5,233,789, U.S. Pat. No. 5,046,283, U.S. Pat. No. 4,887,390 and GB 2 309 500.
In opening and closing a vehicle sliding door it may be desirable for the door to move relatively quickly over the greater part of its travel. As stated above, it should be possible to open the door in 4 to 8 seconds and the same naturally also applies to closing. In order that the door should move quickly it is suitably power-driven in a high gear. A high gear is also desirable for another reason. In view of the risk of crush injuries it is advisable that the door should not close with excessive force. As is well-known, a higher gear produces a smaller force. However, a relatively high force is required in order to finally close the door so that the door locks correctly. In order to obtain a high force it is advisable to power the door in a low gear. It may be desirable, then, to power the door in a high gear for the greater part of the distance travelled by the door between the open and closed position, before then switching to a lower gear when the door nearly reaches its closed position.
U.S. Pat. No. 5,046,283 proposes a power mechanism for opening and closing a sliding door or sliding window on a vehicle, for example. A cable is shown attached to a door and led through the body of the vehicle by way of pulleys, so that the door slides towards an open position when one end of the cable is pulled and towards a closed position when the other end of the cable is pulled. The ends of the cable are wound around a first reel and a second reel, which are arranged concentrically. It is furthermore specified that each of the reels has a large-diameter section on which the cable is wound in order to impart a relatively high speed and low force to the door movement, and a small-diameter section in order to impart a relatively low speed and high force to the door movement over a smaller part of the door travel in proximity to the closed position. It is stated that as a result of this the door can be opened and closed at a high speed over the greater part of the distance travelled by the door between the open and closed position, but that it can move with great force in order to close the door.
In the apparatus described in U.S. Pat. No. 5,046,283, it is stated that the larger diameter section of the reel has a groove 150 for the cable whilst the smaller diameter section of the reel has a groove 160 for the cable. A further groove (ramp groove) 162 joins the larger diameter groove 150 to the smaller diameter groove 160. When the apparatus is in operation, the cable is wound on the helical groove 156 on the larger diameter section. When the door is approaching the closed position the cable goes over the other groove and continued rotation of the reel causes the cable to start being reeled up on to the cable groove situated on the smaller diameter section.
For its function this previously known apparatus is dependent on the cable having moved a certain length, so that a specific length has been reeled up on to or reeled off from a reel. This apparatus must therefore be specially adapted to each type of vehicle in which it is used.
An object of the present invention therefore is to provide an apparatus for opening and closing a vehicle sliding door, which will allow the door to move at high speed over the greater part of the distance between the open position and the closed position and will allow the door to be closed with great force. The apparatus must be easily adaptable to different types of vehicle. A further object is to provide an apparatus, which will permit release in the absence of power, for example. This is a safety requirement in the event of fire, for example. A further object is to provide an apparatus which can easily be retrofitted to various types of vehicle of different sizes and which can furthermore be located at various positions in a vehicle. Another object is to provide an opening and closing apparatus which does not take up as much space and which does not encroach on the vehicle interior.